JP2007524186A - Klystron amplifier - Google Patents

Abstract

A klystron has a plurality of electron beam paths and plural damped disc-shaped cavities. The plurality of electron beam paths cut the cavities and the Klystron amplifier further comprises an annular input cavity and an annular output cavity disposed around the substantially circular external periphery of respective disc-shaped cavities, and in communication with it. The output cavity is arranged to receive RF power from the electron beams, wherein the cavities are arranged to support one of a single resonant rotating wave in a whispering-gallery mode, and a single resonant standing wave in a whispering-gallery mode.

Description

  The present invention relates to a klystron amplifier, a window configuration for a multi-beam klystron amplifier, and a super multi-beam klystron.

  A klystron amplifier, also known herein as a klystron, is a well-known device. There is a current need for high power klystrons with embodiments that can operate in the 900-1000 MHz range while having high power conversion efficiency, strong attenuation of higher order modes, and good lifetime.

  All known designs have drawbacks or deficiencies in one or more of these areas, thus providing a klystron amplifier where each embodiment may be designed to meet the above criteria Should be desirable.

  According to a first aspect of the present invention, there is provided a klystron amplifier comprising means for defining a plurality of electron beam paths and means for defining a plurality of disc-shaped attenuation cavities, wherein the plurality of electron beam paths are connected to each cavity. The crossed and klystron amplifier further comprises an annular input cavity and an annular output cavity disposed about a substantially circular outer periphery of each disk-shaped cavity in communication therewith, the output cavity comprising each electron beam Each cavity receives one of a single resonant rotating wave in the mode with slight leakage and a single resonant standing wave in the mode with slight leakage. Configured to support.

  One embodiment further comprises a wall defining a substantially disc-shaped cavity, the wall having one or more openings for coupling electron beam energy, the cavity wall being a substantially annular input guide. Having a substantially circular perimeter that allows coupling to a wave tube or output waveguide, said coupling being provided by a plurality of windows distributed along the perimeter of the disk-shaped cavity.

  Each window may comprise a ceramic member secured to the waveguide wall.

  One embodiment may comprise an input cavity, two gain cavities, a second harmonic cavity, and an output cavity.

  In one embodiment, the at least one cavity has an RF absorber member disposed within the cavity.

  In one embodiment, each cavity has a vacuum hole.

  In one embodiment, the hole is axial.

  In one embodiment, the hole is about 40 cm in diameter.

  One embodiment of a klystron has a circular RF absorber member.

  In one embodiment, the absorber is made of SiC and is positioned on the outer periphery of the hole so that the mode of operation of the cavity is not substantially affected, and extends a small amount outward from the hole.

One embodiment is configured to operate in TM _{m, n, q} mode.

  In one embodiment, m = 11.

  One embodiment has a plurality of beam tubes.

  One embodiment has one focusing solenoid per beam tube.

  One embodiment is configured to operate in the frequency range 900-1000 MHz.

  One embodiment is configured to operate at substantially 937 MHz.

  In one embodiment, the klystron is configured to provide tens of megawatts.

  One embodiment is configured to provide approximately 50 MW.

  One embodiment has a waveguide around each input and output cavity.

  One embodiment is configured to operate with a power conversion efficiency of greater than 65%.

  One embodiment is configured to operate with a power conversion efficiency greater than 70%.

  In one embodiment, the transverse beam spacing within the cavity is about half a wavelength.

  In one embodiment, the diameter of the beam pipe is small.

  In one embodiment, the diameter is about 1/16 of the operating wavelength.

One embodiment has a common vacuum pump and is configured to operate at 10 ⁻⁸ mbar or less.

  According to a second aspect of the present invention, there is provided a klystron amplifier having a wall defining a substantially disc shaped cavity, the wall having one or more openings for coupling electron beam energy; The cavity wall has a substantially circular outer periphery that allows coupling to a substantially annular input or output waveguide, the coupling being distributed along the outer periphery of the disk-shaped cavity Introduced by several windows.

  According to another aspect of the present invention, there is provided a super multi-beam klystron comprising the klystron according to the first or second aspect, wherein there are a plurality of sets of beams, each set having a plurality of beams, each set being respectively Intersects each cavity at the opening.

  Exemplary embodiments for the present invention will now be described with reference to the accompanying drawings.

  The features of klystrons are fairly well known, and in current experience, klystrons that can deliver high power with high efficiency are best implemented as multi-beam klystrons. This is because by increasing the number of beamlets in the klystron, it is possible to reduce the power per beamlet, thereby lowering the current density and providing sufficient perveance per beam. This is because it becomes lower. The beam perveance, which is a value obtained by dividing the current perveance by the voltage 3/2, has a strong influence on the power conversion efficiency.

  It has been shown that for devices with very low perveance, efficiencies in excess of 80% may be obtained.

  Thus, the multi-beam klystron was selected for the desired application as needed. In the design frequency range, commercially available solid-state RF amplifiers are available to serve as input power sources, and these solid-state RF amplifiers can reliably generate 300 W. In one embodiment for providing 50 MW peak output power, this requires a total gain of 53 dB for the klystron RF structure. This embodiment then typically consists of five cavities: an input cavity, two gain cavities, a second harmonic cavity, and an output cavity.

  Referring to FIG. 1, a multi-beam klystron (1) includes a number of beam tubes (51) arranged in a substantially circular path around a central axially arranged vacuum channel (56). Prepare. Each of the beam paths extends in the longitudinal direction of the klystron (1) from a respective cathode (55) located at the bottom of the klystron (1) to a common collector (60) located at the upper end of the klystron (1). It is confined within each beam tube (51).

  Each electron tube opens close to the bottom of the klystron (1) into an input cavity (101) that will be described more fully herein below with respect to FIG. An input waveguide (102). Each beam tube (51) extends from the upper side of the input cavity (102) to a second harmonic cavity structure (54) (which will also be described more fully herein) to provide a second harmonic. Opening from the upper side of the cavity (54) to the lower wall of the first gain cavity or bunch cavity (53). Subsequently, the beam tube opens from above the first crowd cavity (53) into the second gain cavity or crowd cavity (52). This beam tube continues from the top wall of the second cluster or gain cavity (52) to the output cavity (201). A common collector structure (60) extends upward from the top wall of the output cavity (201). The output cavity (201) has an output waveguide (202) associated with it.

  Solenoid coils (61) are placed around each of the beam tubes to focus the beam within each beam tube.

Each of the input cavity (101), output cavity (201) and cluster (52, 53) cavity includes a respective fine tuning member (621-62d) and a respective RF absorber (64a- 64d). These will be described more fully later herein. In this embodiment, the common vacuum channel (56) is aspirated by a common vacuum pump (150) adapted to provide a good vacuum level, typically below 10 ⁻⁸ mbar.

  Considering the common vacuum channel (56) as the vertical axis, each of the cavities, namely the input cavity (101), the second harmonic cavity (54), the crowded cavity (52, 53) and the output cavity (201) are neutral. Parallel to each other and within each horizontal plane. A high voltage ceramic seal (66) supports a member (67) for mounting each cathode (55).

  Next, four different klystron cavity configurations will be compared (see FIG. 2). Figures 2a and 2d show modes in a disk-shaped (radial) cavity, while Figures 2b and 2c represent modes in an annular (waveguide type) cavity. These modes have very different R / Q values (R / Q indicates the square of the voltage seen by the beam for a given energy stored in the cavity).

One conventional MBK has a simple TM _0.1,0 (pillbox) cavity. In each embodiment of this conventional design, each beamlet (usually between 6 and 30) is in close proximity to the central maximum of the axial electric field at various angular positions (and possibly various radials). Pass through the cavity at position). When using these devices, very high efficiency (80%) has been shown, but has been achieved for relatively low RF power levels (tens of kW). To obtain higher power from this device, the beam current would need to be increased, but because of this geometry, the current is immediately limited by both space charge effects and cathode loading. The

One scheme for this limitation is to change the cavity operating mode to a higher radial index mode—one known device, eg 1.3 GHz, 10 MW, 6 beam MBK, Use TM _0,2,0 mode (see FIG. 2a). Other schemes have been studied for 1.5 GHz, 2 GW, 10 beam MBK. This design was based on the lowest order mode of the ring cavity (see FIG. 2b).

Finally, 150 MW, X-band, 6-beam MBK was proposed by other teams and was based on TM ₁₂ , 1, ₀ waveguide mode (see FIG. 2c).

Since for all values from n = 3, TM _{m, 1,0} (m = 11) has been found to be more efficient than TM _{0, n, 0} , the present invention provides a disc-shaped cavity. Each preferred embodiment uses a high-azimuthal-order TM _{m, 1,0} mode. One embodiment has 27 beams (see FIG. 3d). In this device, the total number of beamlets is equal to approximately twice the exponent m of the operating mode.

  Another very important issue for MBK design is the parasitic mode spectrum. It is absolutely necessary to strongly attenuate the higher-order mode (HOM). In operation, the currents of the individual beamlets are generally not precisely balanced and self-excited to any parasitic mode with a corresponding angular current profile, i.e. a parasitic mode frequency sufficiently close to the operating frequency. There will be danger. If the mode of operation is at the cutoff frequency of the waveguide and the resulting HOM spectrum is so dense that it is difficult to apply any attenuation technique and device as shown in FIG. As shown in FIG. 2a, it is clear that it is particularly critical for each device.

  That is, it can be seen that each device in FIGS. 2a and 2b has severe limitations for high power applications and therefore further discussion is limited to each device as shown in FIGS. 2c and 2d.

A comparison of the TM _{m, 1,0} mode impedances shows that the impedance in both cases is the same for an azimuthal index of about 10. However, disc cavities have a much denser spectrum compared to annular cavities. It appears that there is no easy way to attenuate the HOM of the annular cavity, since the attenuation must be non-resonant, so that means such as choke trapping are not applied. On the one hand, the electromagnetic field pattern of the mode of operation in the disc cavity allows the use of an RF absorber (64) to provide a disc damping cavity, which will be further described later herein with respect to FIG. It will be. It has been shown that the mode spectrum of the TM _{m, n, q} mode (the “slightly leaking” mode) with large m can be easily made very low density. As is known to those skilled in the art, the main feature of the mode with slight leakage is that the majority of the energy is present at or close to the outer wall of the curved cavity or waveguide. is there.

  With reference to FIGS. 3a and 3b, the shape of the input cavity (101) and output cavity (102) will now be described more fully. FIG. 3a shows a vertical cross section through an exemplary cavity along a plane passing through the axis. FIG. 3b shows a horizontal section through the cavity along line b-b '.

  Referring to both figures, each of the cavities (101, 102) is defined by a generally closed generally cylindrical wall (110), and a generally circular lower wall portion (111). It will be appreciated that a structure having a generally circular upper wall portion (112) and a cylindrical peripheral wall portion (113) is formed. The peripheral wall portion (113) allows for the transmission of electromagnetic energy (em energy) through the peripheral wall via one or more so-called “windows” described later herein. In one embodiment, there are a number of multiple small windows, as will be described later herein.

With further reference to FIGS. 3a and 3b, the lower wall portion (111) is shown to have a central hole (113) with a circular opening for connecting a common vacuum channel (56). Around this hole, for example, a SiC circular RF absorber member (64) is disposed, and this member extends outward from the hole (113) by a small amount. The outer radius of the RF absorber member (64) is such that the mode of operation of the cavity is virtually unaffected. The function of the RF absorber is to reduce the higher order radial index modes. In one embodiment, the SiC absorber ring was placed in a position that reduced the Q value in the operating mode by 10% from 3.3 × 10 ⁴ to 3.0 × 10 ⁴ . The Q values for all modes with a radiation index greater than 3 were reduced to values greater than 1000 in the investigated frequency band. It is assumed that reducing the Q factor by about 100 is sufficient to eliminate any effect on the beam. The top wall portion (112) similarly has an axial circular hole (114) surrounded by a fine tuning member (62) for frequency tuning. The upper wall portion and the lower wall portion (111, 112) are each mainly planar, but each wall is a concentric annular region (111a, 112a) recessed inward to connect the beam pipe (51). At the same radial position.

  In the discussed embodiment, the diameter of the beam pipe is small (about 1/16 of the operating wavelength) and utilizes a low single beam current and a low frequency. As a result, the electromagnetic field at the periphery is attenuated very rapidly, thus resulting in a quasi-rectangular longitudinal electric field distribution. Again, the electric field remains very constant within 0.1% over the beam waist (λ / 32). To some extent (as seen from each single beam), it can be seen that the disc attenuating cavities (101, 201) behave like a grid gap.

Due to the fact that the transverse beam spacing in the cavity is about half a wavelength (about 16 cm), the space charge effect between the beams is minimized. A good level of vacuum is required (10 ⁻⁸ mbar or less) to avoid beam instability due to ionization of surplus gas. The disc damping cavity, unlike other geometric shapes, may be pumped very well by attaching a high vacuum conduction hole (about 40 cm in diameter) in the center of the cavity. For the gain / crowd cavity (52), the cavity impedance may be adjusted to the required value by carefully sizing the RF absorber.

  A klystron cavity typically operates in a standing wave (SW) state. In some devices, the output cavity is a traveling wave structure in which energy propagates longitudinally. However, when using a disc damped cavity in an embodiment of the present invention, a resonant rotating wave (RW (rotating wave)) state is established and the rotating wave is shifted by a quarter period in space and time. It may be viewed as a superposition of two standing waves. The resulting wave travels in a rotational mode along the external cavity wall. The complex amplitude of the electric field of the disc attenuation cavity in the SW and RW (rotating wave) states is shown in FIGS. 4a and 4b.

The RW (rotating wave) state provides certain advantages. First, the number of beamlets is now decoupled from the azimuth index of the operating mode and may be arbitrarily selected as in the TM _{0, n, 0} mode. In each embodiment, the number of selected beamlets is an odd number, thus coupling the beam current to each mode having the closest azimuth index will be further reduced. In each test, compared to SW, the RW (rotating wave) condition reduces the single beam current by 25% for the same mode of operation, ensuring higher efficiency.

  As will be described later with reference to FIG. 5a, in each embodiment, the coupling to the input and output cavities is performed by a rectangular waveguide (304) that runs around the entire cavity (302). The feeder cutoff frequency (waveguide width) is chosen so that the wave phase velocity in both the waveguide and the cavity is the same at the operating frequency. As will be described later with reference to FIGS. 5a and 5b, coupling to the cavity (302) is via a number of small coupling holes (320) in the wall (301) between the cavity and the waveguide (304). Done. In a preferred embodiment, the distance between each coupling hole is equal to a quarter of the operating mode wavelength, so the total number of holes is 4 × m. Such a configuration provides good alignment to the cavity and reduces the probability of breaking.

  Turning now to FIG. 5, the preferred embodiment window configuration will now be described. The klystron ceramic output window is probably the most sensitive RF component in the overall system. For example, 10 years of statistics show that about 25% of all klystron malfunctions were due to the destruction of the RF window. In the described embodiment, the concept of a small window of several megawatts is used to take advantage of the features of the disc damped cavity mode of operation.

  A “window” is effectively a series of many small windows, each covering an individual coupling hole as shown in FIG. 5a. Each single small window (320) is first brazed to its own support (322) and then electron beam welded or clamped to the inner wall (301) of the waveguide (304). The typical dimensions of a ceramic disk are 2 mm thick and about 30 mm in diameter. The electromagnetic field configuration of the disk attenuating cavity is such that there is no significant electric field at the position of the small window. In the RW (rotating wave) mode, the local power flow density will be dramatically reduced when using 4 × m small windows. For example, if m = 11 and P = 50 MW, only 1.14 MW will be transmitted through each window. Each embodiment has high reliability. Following the MBK RF configuration, a system of individual solenoids (61) for each beamlet is used. As an example, to control a beam of 150 kV and 15 A each, a focusing magnetic field of 600 G to 700 G is required. Conventional solenoids require about 1 kW per beamlet, which reduces the overall klystron efficiency. In an alternative embodiment, a PPM focusing method is used, similar to that developed for SLAC X-band klystrons.

  The current density is a parameter that determines the cathode configuration. The current density is exponentially proportional to temperature and inversely proportional to the exponential function of the cathode material work function [Richardson-Dashman equation]. In order to keep the beam compression as low as possible, it is desirable to increase the cathode loading, but this should increase the surface temperature and shorten the lifetime. In order to reduce the operating temperature, an alkaline earth metal oxide such as barium or strontium is added to the tungsten cathode. The lifetime of a klystron is essentially determined by the end-of-life emission of the cathode as a result of barium depletion at the cathode surface.

  Conveniently, the klystron has been divided into separate beamlets that may be considered as stand-alone klystrons in parallel, so that in some embodiments, an individual collector is used for each beamlet. There is also. However, when about 30 small collectors are connected in parallel to a common water supply, the cooling of such devices appears to be complex and expensive to manufacture. Important design parameters for the collector are the average power and peak power dissipated, and the surface area on which the electron beam impinges. The minimum amount of cooling water (turbulent flow) required is generally estimated at 3 liters / minute per kilowatt of average RF power dissipated. As a result, and as shown in FIG. 1, in a preferred embodiment, a common collector (60) with each beam allowed to pass through its own pole piece at the output end of the tube and expand in this field free region. ) Is used.

  The overall gain (ratio of peak output power to input drive power) will determine the minimum number of cavities required. If a small bandwidth, eg ± 3%, is required, all gain cavities may be assumed to be tuned to approximately the same fundamental frequency and not stagger tuned.

Referring to FIG. 6, a second harmonic cavity is used to improve the cluster efficiency and thus the klystron efficiency. In one embodiment, the second harmonic cavity structure (54) defines a set of individual TM _0,1,0 second harmonic cavities (501) for interacting with any single beamlet ( 500).

  The foregoing embodiment is represented by a multi-beam klystron having 27 individual mini-klystron sectors, each of which takes about 4% of the total power available from a common output cavity. appear. Each single sector may effectively be treated as an individual device.

  Referring to FIGS. 7a-7c, instead of using a single beamlet in this sector (FIG. 7a), the second embodiment behaves like a mini MBK, thus super MBK (SMBK: Super A plurality of mini-beamlets are used to create (MBK). In this situation, the magnetic system as well as the second harmonic cavity remain unique for every mini MBK or sector.

  Such SMBK may have one of two configurations. The first scheme (FIG. 7b) uses a beam pipe with a larger radius that can contain at least six mini beamlets. In this configuration, the annular beam may also be considered a very good candidate, but unfortunately the second harmonic cavity is somewhat inefficient. The second scheme (FIG. 7c) uses an individual beam pipe for each mini beam. In this example, six mini-beams and thus six mini-beam pipes are shown.

  It can be seen that when using SMBK, a significantly lower cathode voltage may be used (about 2 times) and only a single beam current about 3 times lower is required.

  Modulators that supply long voltage pulses (approximately 100 μs) to either MBK or SMBK devices produce the same peak beam power. However, each beam voltage level is different from each other. If a classic modulator using a pulse transformer is considered, the low voltage system allows for a faster rise time because fewer turns are required on the secondary winding. The pulse transformer is also more compact due to lower volt-seconds, reducing both the leakage inductance and self-capacitance of each winding. This improves the pulse response time and energy efficiency by reducing losses at the rise and fall of this voltage pulse. However, the voltage levels for both MBK and SMBK are significantly lower than for an equivalent single beam klystron with the same output power, pulse width and duty cycle.

  Several embodiments of klystrons embodying the present invention have been described herein. However, the invention is not limited to any of the features of each embodiment, but instead extends to the full scope of the appended claims.

It is a side view of the klystron which implements this invention. FIG. 6 is a diagram showing possible electromagnetic field distributions for a klystron cavity. FIG. 6 is a diagram showing possible electromagnetic field distributions for a klystron cavity. FIG. 6 is a diagram showing possible electromagnetic field distributions for a klystron cavity. FIG. 6 is a diagram showing possible electromagnetic field distributions for a klystron cavity. It is sectional drawing of the disk shaped cavity of the klystron of FIG. It is sectional drawing of the disk shaped cavity of the klystron of FIG. It is a figure which shows the electromagnetic field distribution about the standing wave operation mode of an input / output cavity, and the rotation wave operation mode of an input / output cavity. It is a figure which shows the electromagnetic field distribution about the standing wave operation mode of an input / output cavity, and the rotation wave operation mode of an input / output cavity. FIG. 5 shows an output cavity with a plurality of windows through the output waveguide and details of the window attachment. FIG. 5 shows an output cavity with a plurality of windows through the output waveguide and details of the window attachment. FIG. 2 is a diagram illustrating a second harmonic cavity member for use with the klystron of FIG. 1. It is a figure which shows the electromagnetic field pattern of the 2nd klystron which implements this invention. It is a figure which shows the electromagnetic field pattern of the 2nd klystron which implements this invention. It is a figure which shows the electromagnetic field pattern of the 2nd klystron which implements this invention.

Claims (30)

  A klystron amplifier comprising means for defining a plurality of electron beam paths and means for defining a plurality of disk-shaped attenuation cavities, wherein the plurality of electron beam paths intersect each of the cavities, and the klystron is in communication therewith. Further comprising an annular input cavity and an annular output cavity disposed around a substantially circular perimeter of each of the disc-shaped cavities, wherein the output cavity is configured to receive RF power from an electron beam, A klystron amplifier wherein each cavity is configured to support one of a single resonant rotating wave in a mode with little leakage and a single resonant standing wave in a mode with little leakage.   A klystron further comprising a wall defining a substantially disk-shaped cavity, the wall having one or more openings for coupling electron beam energy, the cavity wall being a substantially annular input guide. A substantially circular outer periphery that allows coupling to a wave tube or output waveguide, wherein the coupling is provided by a plurality of windows distributed along the outer periphery of the disc-shaped cavity. Item 10. The klystron according to item 1.   The klystron according to claim 2, wherein each window comprises a ceramic member secured to a waveguide wall.   The klystron according to claim 1, comprising an input cavity, two gain cavities, a second harmonic cavity, and an output cavity.   The klystron according to claim 1, wherein the at least one cavity has an RF absorber member disposed therein.   The klystron according to claim 1, wherein each cavity has a vacuum hole.   The klystron according to claim 6, wherein the hole is in an axial direction.   The klystron according to claim 6 or 7, wherein the hole has a diameter of about 40 cm.   The klystron according to claim 6, 7 or 8, comprising a circular RF absorber member.   10. The klystron according to claim 9, wherein the absorber is made of SiC and extends outwardly from the hole by an amount such that the mode of operation of the cavity is substantially unaffected. 11. The klystron according to claim 1, wherein the klystron is configured to operate in a TM _{m, n, q} mode.   The klystron according to claim 11, wherein m = 11.   The klystron according to claim 1, comprising a plurality of beam tubes.   14. A klystron according to claim 13 having one focusing solenoid per beam tube.   A klystron according to one of the preceding claims, configured to operate in the frequency range 900-1000 MHz.   16. A klystron according to one of claims 1-15, configured to operate substantially at 937 MHz.   17. A klystron according to one of claims 1-16, configured to provide tens of megawatts.   The klystron of claim 17 configured to provide about 50 MW.   19. A klystron according to claim 1, comprising a waveguide around each input and output cavity.   20. A klystron according to claim 1 configured to operate with a power conversion efficiency of greater than 65%.   21. The klystron of claim 20 configured to operate with a power conversion efficiency greater than 70%.   The klystron according to one of claims 1-21, wherein the transverse beam spacing in the cavity is about half a wavelength.   23. The klystron according to claim 1, wherein the beam pipe has a small diameter.   24. A klystron according to claim 1, wherein the diameter is about 1/16 of the operating wavelength. 25. The klystron according to one of claims 1-24, having a common vacuum pump and configured to operate at 10 < ^-8 > millibar or less.   A klystron having a wall defining a substantially disc-shaped cavity, the wall having one or more openings for coupling electron beam energy, the cavity wall being a substantially annular input waveguide. A klystron having a substantially circular perimeter that allows coupling to a tube or output waveguide, wherein the coupling is provided by a plurality of windows distributed along the perimeter of the disc-shaped cavity.   27. The klystron of claim 26, wherein each window comprises a ceramic member secured to the waveguide wall.   28. A super multi-beam klystron comprising a klystron according to one of claims 1-27, wherein there are a plurality of sets of beams, each set having a plurality of beams, each set intersecting each cavity at a respective opening. Super multi-beam klystron.   29. A super multi-beam klystron according to claim 28, comprising a plurality of beam tubes, each beam carrying a plurality of mini-beams.   29. A super multi-beam klystron according to claim 28, comprising a plurality of beam tubes, each beam carrying a single mini beam.

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